Disease or trauma of the vestibular sensory organs often occur, leading to acute vestibular pathology followed by chronic central compensation. Central compensation takes place in the vestibular nuclei neurons that receive information from the semi-circular canals and otolith organs in the vestibular labyrinth. These neurons process the information into a coded output signal that provides for the vestibular and vestibulospinal reflexes, as well as the conscious perception of the head and body in space. It is surprising to find that although many investigations have reported on the responsiveness of vestibular nuclei neurons to stimulation of the peripheral vestibular organs, it has not yet been possible to determine how these neurons process afferent information from the different semicircular canals into an integrated output signal. Since information from the vestibular nuclei is presented to different brain regions associated with differing reflexive and sensory functions, it is important to understand the mechanisms used by vestibular neurons to produce a signal that is relevant to the projected target's function. The proposed studies will, for the first time, examine the response properties of vestibular nuclei neurons to dynamic stimulation of individual semicircular canals. The specific activation of each semicircular canal organ will be produced by a unique mechanical stimulation technique that was recently developed in my laboratory. Separate afferent inputs to the vestibular nuclei neurons will, therefore, be individually manipulated allowing the quantitative mechanisms of information synthesis in these neurons to be delineated using electrophysiological recordings. In order to determine the projection patterns and morphology of vestibular nuclei neurons, antidromic activation and intracellular staining with horseradish peroxidase will be obtained in cells that were previously physiologically characterized with orthodromic electrical and mechanical stimulation of the semicircular canals. Comprehensive data regarding the morphological and physiological characteristics of vestibular nuclei neurons will allow direct structure-function relationships in the central vestibular system to be derived. Before more effective treatments of vestibular system disorders ca be realized, relevant knowledge about information coding in vestibular nuclei neurons must be acquired.